1. Field of the Invention
This invention relates to a method for treatment of effluent with activated sludge in suspension for removal of nitrogen and phosphorus and for simultaneous stabilization of the sludge and to a continuously charged apparatus for the execution of this method. This invention also relates to an apparatus having a compact effluent treatment reactor, particularly for individual effluent disposal, in which an activated chamber and a settling tank are combined in one internal sludge cycle, and the activated chamber containing a non-ventilated anaerobic fermentation zone and a denitrification zone as well as a ventilated nitrification zone.
2. Discussion of Related Art
Various designs of small and very small activated-sludge plants have been developed for the treatment of locally accruing effluent from fairly small sources of water contamination. A substantial goal is to create a small, but powerful and economically viable plant, which can overcome enormously variable flows of volume and mass.
If systems for individual effluent disposal in rural regions form a real alternative to central treatment systems, they should guarantee a comparable treatment for the removal of nitrogen and phosphorus from the effluent, at similar operating costs as well offering simple operation.
To remove as much nitrogen as possible, it is necessary for the sludge load to be as small as possible. Attempts are made to work with as large as possible a quantity of activated sludge in aeration tanks. The known, relatively flat reactors of small effluent treatment plants do not allow for operation with very high concentrations of sludge. Where there are higher concentrations of activated sludge, the sludge level is increased in the settling tank; where this sludge is sucked-off in an intensive manner into a denitrification zone. However, there is also an increase in the undesired dissolved oxygen in this zone and the residence time of sludge under anoxic conditions is reduced.
The biological removal of phosphorus is often effected by an anaerobic zone in the activation chamber, and it is possible to increase the efficiency of this process by an anaerobic fermentation zone connected upstream. The phosphorus, which is bound in the activated sludge, is subsequently discharged together with surplus sludge in the oxic state. In the apparatuses known to date, phosphorus cannot be removed effectively in a biological manner, as the crude effluent, which is supplied to the small effluent treatment plants, has not been pre-fermented in the same way as the effluent originating from numerous sewer pipe networks, and as the existing reactors for the treatment of locally occurring effluent have no conditions for this type of fermentation.
In known effluent treatment systems, in which the activated sludge method is applied in continuously charged systems, the concentration of the activated sludge can be increased. Because of the danger of congestion or respectively because it is not possible to have a high degree of control of the treatment process, fixed bed systems frequently give rise to problems.
The crude effluent from small sources of water contamination contains many coarse substances and in the majority of cases is loaded with fat. The mechanical removal of coarse substances from the effluent is effected in the sewage trap, which frequently operates with ventilation, or large bubbles, however this only disintegrates a small portion of the sewage substances, particularly with respect to the short residence time of the effluent in this part of the reactor. Coarse sewage particles and organic substances which do not decompose easily, progress into other parts of the reactor and sometimes even progress into the discharge flow for treated water. In known reactors, the protection against the ingress of fat into the nitrification zone is not controlled, giving rise to a reduction in efficiency of the activation.
The cause of the sludge being washed-out and of the reduced effect of the treatment in the designs of the previously known reactors is, among other things, also the unsuitable admission of the activated mixture into the settling tank, which results in the formation of dead zones and uncontrolled turbulence in the settling tank. To avoid the negative influences of the oscillating, hydraulic load of the flat settling tank in the known reactors, the principle of so-called fluid filtration is used, according to which a specific level of sludge is assumed in the settling tank and thus an extensive reduction in the level of treated water in the settling tank. Under these conditions, where there is a lack of qualified operators, the treatment system tends to wash-out sludge and to reduce the efficiency of the treatment. The retaining of the old sludge as well as the high degree of efficiency of the treatment means that a high concentration of sludge can be achieved in the reactor, which is not possible in known reactors using liquid filtration. Uncontrolled denitrification with the sludge being washed-out into the treated water zone is caused by the longer residence time of the sludge in the settling tank with liquid filtration. At the same time, the efficiency of the treatment is lower, as the concentration of the dissolved oxygen in the settling tank is reduced. Even excessive ventilation of the nitrification zone results in the sludge being washed-out, as sludge particles are raised by adhering air bubbles. In the previously known reactors, the washing-out and de-gasification of sludge is frequently achieved by sucking it out at the level of the water-surface into the nitrification zone using air-lift pumps, giving rise to an increase in the hydraulic load of the setting tank and a reduction in the efficiency of the separation. Alternatively, a degasification container or respectively a zone with ventilation can be connected upstream of the settling tank, giving rise, however, to an increase in investment costs. There is also a technical solution according to which the water-surface in the settling tank is ventilated; however, this solution does not prevent the sludge being washed-out in a sufficient manner.
German Patent References DE-C2-3501585, DE-C2-3716-782, DE-A1-3915026 and DE-A1-19737373 and PCT International Publication WO 98/23542 make known methods for the treatment of effluent, where phosphorus or respectively nitrogen is removed from the effluent by activated sludge. The PCT International Publication WO 98/23542 discloses a method, where the concentration of phosphorus is measured at various points in the settling tank and the concentration of the re-circulated sludge, which is supplied to the primary water-sludge mixture or another anaerobic zone, is modified accordingly.
In addition, German Patent Reference DE-C2-3235992 discloses a system for biological treatment and denitrification of effluent with an aeration tank, which is divided into two or more chambers by adjustable partition walls extending at least approximately in the radial direction.
It is one object of this invention to provide a method and an apparatus for biological treatment of effluent with an activated sludge method with the removal of nitrogen and phosphorus while avoiding the identified disadvantages of the known art, the method and apparatus of this invention providing a treatment which is of a high level and is steady and requires minimum investment and operating costs.
This object is achieved through characteristics described in the claims and in this specification.